1. Field of Invention
This invention relates generally to the field of fastening devices and methods of use, more particularly, to threaded fasteners and thread clamping devices, and most particularly to thread clamping devices typically in combination with a bearing plate and other components as a self-adjusting shrinkage compensation device.
2. Description of the Prior Art
Wood is a major construction material in many places throughout the world. Wooden structures frequently use “tie-downs” to secure the wooden structure to its foundation, typically a concrete foundation. The function of tie-downs is thus to secure the wooden structure to its foundation in the presence of forces (perhaps substantial forces) tending to separate the structure from its foundation, such as high winds, seismic events or general shifting and settling of the surrounding earth. However, the wood typically used for construction often has considerable water content when initially installed and with time, the water evaporates and the wood dries out. In the process of drying out, the wood dimensionally shrinks. Approximately 4% shrinkage in the first year following construction of a wooden structure is not uncommon. This shrinkage commonly causes tie-downs to loosen, thereby making the structure more susceptible to damaging displacements in the presence of high winds, earthquakes among other external forces. Catastrophic damage may result.
A common method for implementing a tie-down is by imbedding a vertical threaded rod into the concrete of the foundation at the location where the wooden structure is to be joined to the foundation. The threaded rod generally resides within the walls of a single or multilevel structure as it passes from the concrete foundation up through each floor of the structure. Each floor is typically attached to the threaded rod by a separate tie-down. The primary fastener presently used to implement a tie-down is a standard “hex” nut.
If a standard nut is used, a space will typically develop under the standard nut and above the wood as the wood shrinks in dimension due to loss of water as described above. This space allows the tie-down (and structure) to move vertically when an overturning moment is applied to the structure as might occur, for example, during a seismic event, wind loading, among other circumstances. This motion of the structure with respect to the foundation, in turn, allows for deformation of the structural walls and may produce substantial damage that the tie-down is designed to prevent when functioning properly, that is when holding the structure securely in place on the foundation. Thus, a need exists in the art for a tie-down that is self-compensating, that is, a tie-down that maintains secure attachment of the structure to the foundation despite shrinkage of the wood.
As described in detail below, various embodiments of the present invention relate to thread clamping devices that include movable segments or “nut segments.” Some distinguishing characteristics of some embodiments of the present invention relate to flat (or planar) surfaces on the nut segments contacting flat surfaces on the top and/or end housings of the thread clamping device. Other shrinkage compensation devices having moveable segments include those of Sasaki (U.S. Pat. No. 5,081,811) and Taneichi (U.S. Pat. No. 6,007,284). Related art includes the following U.S. Pat. Nos. 3,695,139; 4,378,187; 4,974,888; 5,324,150; 5,427,488; 5,733,084; 5,988,965; 6,361,260; 6,406,240. However, these devices use frustoconical surfaces to support the nut segments. That is, the surfaces of the nut segment and the surface(s) of the housing that the nut segment is matched against are both conical. This is a disadvantageous structure since (among other reasons) two conical surfaces only match exactly at a single position and at any other position the two surfaces contact only at lines and points. This typically causes high stress concentrations along the lines and points of contact. Also, as the two non-planar surfaces slide relative to one another in a radial direction, the two surfaces are forced apart. This causes non-linear motion of the segments and can cause the segments to jam within the supporting top and bottom structures if insufficient clearance is not allowed. The flat surfaces employed on various embodiments of the present invention reduce or avoid these problems by employing flat surfaces and a structure such that no conical surfaces engage one another. These flat surfaces allow linear segment motion and are easily guided as they move between minimum and maximum radial positions. Also, the use of flat surfaces causes the stress loads to be distributed over the entire flat surface area and thus the local stresses remain relatively low within the thread clamping device pursuant to various embodiments of the present invention. This is true even when sufficient forces are applied so as to force the rod engaged by the thread clamping device to fail in tension.
In addition, a major construction cost is often the cost of labor. Therefore, installation of tie-downs in a manner that reduces labor costs is advantageous. For example, one common requirement when installing tie-downs is that threaded rods be connected together end to end. This is generally accomplished with a machined component having internal threads matching the threaded rod. Often, the threaded rod that comes out of the foundation of the structure is of very short length and another threaded rod is connected to this short rod using a connector. The connector is first turned and threaded onto the projecting end of rod protruding from the foundation and a second rod joined to the first by means of the connector. This requirement to connect two threaded rods is fairly common worldwide, and not specific to the construction industry. This process of connecting two rods, most often performed manually, is time consuming and labor intensive. Thus, a need exists in the art for devices and procedures for the efficient and rapid connection of threaded rods.